Primary hyperparathyroidism induces erythropoietin resistance through fibroblast growth factor 23.

Introduction: Primary hyperparathyroidism (PHPT) often causes hypercalcemia and complications requiring parathyroidectomy (PTX). Anemia affects 15%-50% of PHPT patients, but its mechanisms remain unclear. While parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23) contribute to anemia in secondary hyperparathyroidism through erythropoietin (EPO) resistance and bone marrow fibrosis, their roles in PHPT are less defined. This study explores the effect of PHPT on erythropoiesis by assessing hemoglobin (Hb), EPO, and FGF23 levels before and after PTX.

Methods: In a monocentric longitudinal study (2018-2020), PHPT patients scheduled for PTX were followed for 6 months. Blood and urine samples were collected at baseline (surgery day), at 10 days and 6 months postsurgery. Pearson correlation assessed relationships between Hb, EPO, PTH, FGF23, calcium, and phosphate at baseline and 6 months. Mixed-effects models evaluated the impact of PTH and FGF23 on Hb, adjusting for confounders.

Results: In a cohort of 111 PHPT patients (81% women, median age 64, normal body mass index), anemia prevalence decreased from 9.9% at baseline to 2.7% 6 months post-PTX, despite stable EPO levels. Postsurgery, PTH, FGF23, and calcium significantly decreased. PTH did not significantly correlate with Hb or EPO at any time point. Before surgery, FGF23 negatively correlated with Hb (R = -0.20, P = .020) and positively correlated with log-EPO (R = 0.38, P < .001). Mixed-effects models showed no predictive effect of PTH on Hb. However, multivariable models indicated a significant association between FGF23 and declining Hb (β = -.01, 95% confidence interval [-0.02; -0.01]).

Conclusion: Anemia in PHPT is linked to elevated FGF23 levels, potentially causing EPO resistance.